In the last two decades, opioid analgesics have assumed an important place in general
anesthetic practice in the United States. Part of the reason for this has been the
introduction of the potent new agonists fentanyl, sufentanil, and alfentanil. Because
of problems with morphine-oxygen anesthesia (incomplete amnesia, occasional histamine-related
reaction, marked increases in intra- and postoperative respiratory depression), a
suitable alternative was sought but not found among existing opioids. A breakthrough
came in 1960, when fentanyl was synthesized, laying the foundation for a better understanding
of the structure-activity relationships of narcotic analgesics and stimulating interest
in developing compounds with even greater potency and safety margins. Investigators
interested in opioid anesthesia began to study fentanyl in animals and then in humans.
Fentanyl (50-100 micrograms/kg) with oxygen (100%) was evaluated as an anesthetic
in patients undergoing mitral valve and coronary artery surgery. Changes in cardiovascular
dynamics with induction doses ranging from 8 to 30 micrograms/kg consisted of small
decreases in heart rate and arterial blood pressure. All other cardiovascular variables
studied, including cardiac output, remained unchanged, even with additional doses
up to 100 micrograms/kg. It was determined that fentanyl had use as a narcotic anesthetic,
despite its potential for cardiovascular depression and stimulation, respiratory depression,
muscle rigidity, and, occasionally, incomplete anesthesia. Since the introduction
of fentanyl, two other potent synthetic opioids have been introduced into clinical
practice--sufentanil and alfentanil.